| Polyrhachis orokana|
Nothing is known about the biology of Polyrhachis orokana.
Kohout (2007) - P. orokana is very similar to Polyrhachis impressa, both featuring almost the same sculpture pattern of the mesosomal dorsum, somewhat posteriorly protracted eyes and the concave anterior face of first gastral segment. However they differ in a number of characters, including the shape of the mesosomal-propodeal dorsum which, in orokana is transverse, distinctly wider than long, while in impressa it is as long as wide. The eyes in orokana are convex and protuberant and fully extend beyond the lateral cephalic outline in full face view. In comparison the eyes in impressa are less convex, somewhat sunk into a shallow concavity in the cephalic sculpture and extend only moderately beyond the cephalic outline. The lateral petiolar teeth in orokana are very small and upturned, while in impressa they are relatively long and curved backwards and upwards. The lateral gaster has distinct, horizontally directed, longitudinal striae in orokana; while in impressa the striae are oblique and directed towards the dorso-anterior margin of the first gastral segment.
Keys including this Species
Distribution based on Regional Taxon Lists
Distribution based on specimens
The subgenus this species is a member of, Aulacomyrma, is poorly colected. Kohout (2007) summarized what is known about their biology in a revision of the species in the subgenus. This offers an explanation as to why most Aulacomyrma are known from few collections and specimens. There are only two records of nests being found. A small colony of Polyrhachis dohrni was collected by Kohout from a dry hollow twig on a living tree at the edge of lowland rainforest. The internal walls of the twig cavity were lined with a little silk. Ward collected a nest of Polyrhachis wardi from a dry twig of a rainforest tree. The colonies of both species were rather small, with only a few workers (5 and 11 respectively, including 2 and 3 alate queens and a single male). If such a nesting pattern is the norm for other species of the subgenus, that might explain the general scarcity of Aulacomyrma material even in the best collections. Many Aulacomyrma species are described and only known from a holotype.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- orokana. Polyrhachis (Aulacomyrma) orokana Kohout, 2007a: 231, figs. 84, 87, 90 (w.) NEW GUINEA.
Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.
TL c. 4.94-5.69 (c. 4.94); HL 1.25-1.31 (1.25); HW 1.00-1.06 (1.03); CI 76-82 (82); SL 1.25-1.28 (1.25); SI 121-125 (1.21); PW 0.87-0.90 (0.870; MTL 1.18-1.22 (1.18) (4 measured).
Anterior clypeal margin arcuate, entire; basal margin very weakly impressed, indicated by hairline break in cephalic sculpture. Frontal triangle indistinct. Frontal carinae relatively short, strongly raised with laminate lobes. Sides of head slightly convex in front of eyes, rounding almost immediately into preoccipital margin behind. Eyes strongly convex, situated well back on sides of head, fully protruding beyond lateral cephalic outline. Mesosoma laterally immarginate with dorsum rounding onto sides in unbroken curve; evenly convex in profile. Pronotal humeri armed with somewhat dorso-ventrally flattened, acute teeth; anterior margins dorsally raised; lateral margins continued obliquely downwards and merging on sides with lateral striae. Promesonotal suture distinct, metanotal groove lacking. Mesonotal and propodeal dorsa fused, distinctly transverse, separated from declivity by distinct transverse ridge terminating laterally in rounded prominences. Petiole with acute dorsal margin terminating laterally in very small, upturned teeth. First gastral segment shallowly concave anteriorly, anterodorsal margin of concavity obtuse, not raised above dorsal face of segment.
Sculpture of head and mesosoma consisting of regularly spaced striae, mostly longitudinal on head, converging anteriorly on clypeus. Striation on pronotal dorsum inversely U-shaped anteriorly, becoming widely V-shaped towards promesonotal suture and continuing obliquely onto sides. Mesonotal and propodeal dorsa with almost semicircular striae, extended obliquely along sides. Petiole shagreened. First gastral segment longitudinally striate laterally and dorsally.
Rather short, erect or curved, silvery and off-white hairs on most dorsal surfaces of body, shortest lining dorsal margin of petiole, longest and yellowish on dorsum and apical gaster. Silvery appressed pubescence on pronotal dorsum forming distinct V-pattern, running diagonally from pronotal humeri towards middle and dispersing before reaching promesonotal suture. Pubescence on mesonotal and propodeal dorsa becoming rather dense and somewhat directed medially; sparse on sides of propodeum, dense posteriorly on propodeal lobes and coxae. Propodeal declivity bordered laterally and dorsally with very fine, short, upward curved pubescence. Petiole and dorsum of gaster with fairy abundant pubescence, not obscuring underlying sculpture.
Black. Antennae, femora, proximal ends of tibiae and first tarsal segment very dark to dark reddish-brown, tibiae and tarsi distinctly light yellow.
HOLOTYPE: PAPUA NEW GUINEA, E. Highlands, Orokana, 27.xi.1967, under bark of tree, B. B. Lowery (worker). PARATYPES: data as for holotype (3 workers). Type distribution: holotype in Australian National Insect Collection; 1 paratype each in The Natural History Museum, Museum of Comparative Zoology and Queensland Museum.
Named after the locality Orokana in the Southern Highlands Province of Papua New Guinea.
- Kohout, R.J. 2007a. Revision of the subgenus Aulacomyrma Emery of the genus Polyrhachis F. Smith, with descriptions of new species (pp. 186-253). In Snelling, R.R., Fisher, B.L. and Ward, P.S. (eds). Advances in ant systematics: homage to E.O. Wilson – 50 years of contributions. Memoirs of the American Entomological Institute. 80:690 pp. PDF